There are various routes of drug administration with orally administered drug accounting for about 70-80%. The dosage form for this route is convenient to use, has high therapeutic efficiency coupled with low side effects. Oral dosage forms include tablet, capsules, and other solids. Tablets are nonetheless widely used.
The emergence of controlled released dosage form during the 1940-1950 period offered long acting effect and with concomitant reduction of frequent administration of the drug. A range of drug delivery systems were developed from then on.
Orally controlled released dosage forms usually require the following:
1. Coating of active drug component with low soluble material which should be soluble in the GI tract. PA1 2. Complexation or combination of drug with other components. PA1 3. Drug interaction with ion exchange resins. PA1 4. Mixing of drug with matrix.
Generally drugs have different physico-chemical properties depending primarily on the structure. Excipients like diluents, lubricants, maskers, disintegrants, binders or coloring materials and sweeteners are mixed with drugs for suitability and better oral dosage forms. Injectables dosage forms when used will not pass through the GI tract. Furthermore other dosage forms can be administered through the nose, implantation, transdermal, suppositories or for vaginal application to release the drug slowly.
T. Higuchi in J. Pharm. Sci. 40, 874(1961) tabletted drug, polymer, and other excipients into a matrix type by oral controlled tablet. This kind of controlled dosage form demands a very specialized and complicated manufacturing process. It also needs very special formulation to achieve optimal controlled effect.
A. G. Thombre invented the WPI Patent 94-199917124, controlled release delivery device special capsule containing Osmagent, coated macro-particulate solubility modifier, and active material in asymmetric membrane.
C. Camponeschi et al. invented the WPI Patent 94-169606/21, controlled release composition containing ursodeoxycholic acid. It consist of micro-granules prepared by extrusion-spheronisation containing the drug, a plasticiser, a binder, and optimal disintegrants.
K. L. Branly et al. invented the WPI Patent 93-312854/40, microcapsules with controlled release and improved handling safety-consisting of active core material (e.g. herbicide) encapsulated in glutaraldehyde cross-linked gelatin containing a water-soluble softener.
S. M. Herbig et al. invented the WPI Patent 92-079771/10, devices for controlled release of active agents e.g. drugs, nutrients -have shell comprising interfacially polymerised membrane on porous support surrounding core of active agent.
ELAN Corp. PLC have the WPI Patent 85-110586/19, oral granules for controlled release of methyidopa which comprises core containing acid and external polymeric membrane.
The use of laser to drill holes on drug controlled released system was reported by N. K. Jain in J. Pharm. Sci. 73, 1806(1984). The theory involved the usage of formaldehyde to make the gelatin capsules cross-linked and become GI tract insoluble capsules. The drug eventually will be released through the small holes in the capsule into the dissolution medium and this kind of controlled dosage forms have sustained release effect. The laser drilling on the capsule is not easy to orientate and achieve hence it can not be industrially employed or utilized.